Heart failure is a condition affecting thousands of people worldwide. Essentially, congestive heart failure occurs when the heart is unable to pump blood at an adequate rate to meet metabolic demand Heart failure may result in tissue congestion, peripheral edema, pulmonary edema, and shortness of breath. When heart failure is severe, it can lead to patient death.
Heart failure treatments have historically been pharmacologically based but more recently, biventricular stimulation has been added in moderate to severe heart failure patients meeting approved indications. Drug therapy has included diuretics, beta blockers, angiotensin converting enzyme inhibitors and aldosterone antagonists. Even though patients may follow strict drug regimens, heart failure exacerbations may arise, placing them at risk for increased morbidity and mortality.
Some implantable medical devices assist in detecting medical conditions based on measured impedance. For example, certain implantable medical devices are programmed to measure intrathoracic impedance of a patient. The intrathoracic impedance may be a function of the amount of fluid within the thoracic cavity of the patient. The amount of, or change in, the amount of fluid within the thoracic cavity may be indicative of various cardiac conditions. For instance, a relatively large amount, or a relatively significant change from the patient's average amount, of fluid within the thoracic cavity may be indicative of an acute heart failure event.